In radio communication systems such as mobile communication systems, plural base stations, each which establishes a relay between a radio link and a cable link, are installed and the radio wave service areas provided by them are overlapped. That feature provides a communication service enabling communications between mobile stations existing in a broad physical area other mobile stations. If the quality of radio waves transmitted from a mobile station is not sufficient in the place where a mobile station exists, the communication quality will be deteriorated. In some situations, such quality deterioration may cause out-of-synchronization between a base station and a mobile station, thus resulting in abnormal disconnection of the radio link. Communication troubles, such as abnormal disconnection, largely deteriorate conveniences to users and discomfort users, thus finally leading to cancellation of service contracts. Therefore, the network performance monitoring process that monitors the frequency of occurrence of abnormal disconnection is now essential to communication carriers.
Non-patent document 1 discloses the performance monitoring items in the third generation UMTS (Universal Mobile Telecommunications System) standardized in the 3GPP (third generation Partnership Project). In the section 4.2 of non-patent document 1, the method is disclosed for accumulating and recording the number of times of release for each release reason of radio access bearer (RAB). Section 9.2.1.4 of non-patent document 2 tabulates concrete release reasons. For example, by using accumulated values of “Radio connection with UE lost” shown as the release reason 46, you can grasp the number of times of abnormal communication termination due to disconnection of a radio link.
Non-patent document 1 discloses the method for measuring a bit error ratio of received signals in a communication channel, in a mobile station or base station; generating alarm that informs a user of the detection when the bit error ratio of a predetermined value or more is detected continuously a predetermined number of times; and forcibly disconnecting the communication channel when the alarm continues an elapsed time.
Patent document: Patent publication No. 2910980 (FIG. 1, Page 4)
Non-patent document 1: “Performance measurements-UMTS and combined UMTS/GSM(TS32.403) V4.10.0”, 3GPP, March in 2005, pp.
Non-patent document 2: “UTRAN Iu interface Radio Access Network Application Part (PANAP) signaling (TS 25.413) V3.14.0”, 3GPP, September in 2003, pp. 23, 60, 83-90